| Studies were conducted to determine the changes in the following soil properties after sludge additions: pH, CEC, organic and inorganic carbon content, and properties of the soil humic substances. Cadmium solid phase chemical forms, and cadmium adsorption in the sludge amended soils were determined.;A sequential extraction procedure was devised and tested for correspondance to the appropriate cadmium chemical forms. The new procedure consisted of extracting the soil with 1 M NH(,4)NO(,3) (soluble + exchangeable), 3 times with 1 M NH(,4)Cl (carbonate bound), 0.2 M Cu(NO(,3))(,2) (organic bound), and 1 M HNO(,3) (residual). Cadmium existed mainly in the carbonate and organic bound forms (70-80%), with <1% in the exchangeable fraction. The cadmium chemical form was dependent on the sludges' chemical treatment and soil texture. Cadmium chemical forms did not show any changes up to 8 years after sludge additions were discontinued.;Adsorption of cadmium by the soils was best fitted with the Freundlich equations. Sludge addition increased the cadmium equilibrium exchange constant, and adsorption maxima. Selectivity of the soils for cadmium was dependent on the soil type, sludge treatment, and solution cadmium concentration.;Application of sludge altered neither the elemental composition nor the carboxyl acidity of the humic materials, but led to an increase in the total and phenolic hydroxyl acidity. IR spectra did not show any differences in the humic materials after sludge additions, while NMR spectra indicated an increase in aliphatic and a decrease in aromatic carbons. Conditional stability constants (K') and binding sites (BC) for cadmium humic complexes were unchanged for the strong binding sites (log K' = 4.9, BC = 16 (mu)mol/g) after sludge additions, but log K' decreased (3.0 vs 3.7) and BC increased (200 vs 50) for the weak binding sites.;Conestoga loam and Caledon loamy sand soils were amended with three sludges (treated with lime (Ca-sludge), FeCl(,3) (Fe-sludge), and AlCl(,3) (Al-sludge)) from 1973 to 1980. Addition of the sludges led to the following changes in the soil: (1) an increase in pH for the Ca-sludge and a decrease for the other sludges; (2) an increase in carbonates for the Ca-sludge, but not the other sludges; (3) an increase in organic matter for the Al and Fe sludges, but not the Ca-sludge; and (4) an increase in total and pH-dependent CEC for all the sludges. |
